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A collection of Streptomyces spp. isolated from the rhizosphere soils of 14 Thai medicinal plants were found to produce, the plant growth hormone indole-3-acetic acid (IAA) in a yeast malt extract medium supplemented with 2 mg/mL L-tryptophan. Streptomyces CMU-H009 recovered from soil associated with lemongrass (Cymbopogon citratus) was very effective in producing IAA. Based on the 16S rDNA sequence analysis, this strain was most closely related to Streptomyces viridis NBRC 13373T (99.3% similarity). The IAA production was maximums (300 mg/mL) when the strain CMU-H009 was cultivated in a yeast malt extract broth amended with 2 mg/mL L-tryptophan a pH 7.0, and incubated at 30 o C with shaking at 125 rpm for 3 d. The culture filtrate from the strain CMU-H009 stimulated a significant increase in the germination and root elongation of maize (Zea mays) and cow pea (Bruguiera parviflora) seeds. The IAA from this strain was extracted, purified and identified by thin layer chromatography.
Khamna et al. (Fri,) studied this question.